1. Field of the Invention
The present invention relates to an LED and an attachment structure of an LED which prevent heat accumulation safely and effectively, which can clamp the voltage of the surface of a can, and which allow electrically safe mounting.
2. Description of the Related Art
LEDs have a variety of applications as light emitting elements. Though there are several types of LEDs, such as a resin mold type and a can type, an ultraviolet LED, for example, is greatly deteriorated by ultraviolet light, and emits a large amount of heat, while output is lowered as the quality of resin changes in a resin mold type, and therefore, types that are reliable for a long period of time are limited to the can type. This can type is provided with an LED pedestal surrounded by an anode, a cathode and a reflector within a housing, where at least the connection ends of the anode and the cathode are led out of the housing, in a manner where a voltage is applied between the anode and the cathode via these connection ends, for light emission from the interface between the PN layers of the LED element placed within the housing. This light is reflected from the reflector so as to be guided to a transparent portion made of glass which is attached to the housing, in the configuration of the can type LED. The housing is generally made of a metal.
In such a can type, it is difficult to avoid deterioration in the light emitting property caused by the heat transmission and heat accumulation accompanying light emission, as well as negative effects on durability and longevity caused by heat stress. According to the prior art, however, no examples are cited where a heat radiation structure is actively adopted.
FIG. 14 illustrates an illumination device 1 for product inspection which is appropriate for use in the case, for example, where products are inspected using reflected illumination. This illumination device 1 is formed of a surface 1a for mounting light emitting bodies in a curved concave form, such as the inner surface of a cylinder or the concave surface of a cone, and of a great number of LEDs 2, which are densely mounted on this surface 1a for mounting light emitting bodies without intervening space.
However, it has conventionally been thought that it is difficult to provide a heat radiation structure on the rear surface of surface 1a for mounting light emitting bodies which curves in this illumination device 1. Therefore, no specific heat radiation member is provided behind LEDs 2 but providing an air layer AS that intervenes between LEDs 2 and a frame member 1b, which merely allows natural heat radiation toward this air layer AS (Japanese Unexamined Patent Publication No. 10-21729).
Therefore, a structure that makes active heat radiation possible has been examined, wherein, as shown in FIGS. 11 to 13, a housing 21 placed beneath a transparent portion 21x which forms an LED2 is formed of a material having a high thermal conductance, and one of connection ends a1 and k1 of an anode A and a cathode K is made to make metallic contact with housing 21 in one of lead positions 21a and 2lk (21k in the figure) provided in housing 21, so that heat can be radiated to the air from housing 21. Though in this example, a reflector R conceptually works as the above described cathode K which conducts to a body 21b of the housing, reflector R may be formed in housing 21 by means of digging in a manner where the structure allows cathode K to be mounted in a mounting hole provided in body 21b of the housing. In this case also, reflector R, housing 21 and cathode K are in a condition where they are mutually conductive. In the figures, symbols 10a and 10b indicate wiring patterns. The same effects as in such a structure can be gained in the case where the anode A side is made to conduct to reflector R and housing 21.